The present invention relates to boring tools in general, and more particularly to improvements in boring tools of the type wherein the head of a boring bar or analogous holder supports adjustable carriers for boring bits. Still more particularly, the invention relates to improvements in boring tools wherein the head of the boring bar has teeth mating with complementary teeth of the bit carriers and wherein the carriers are formed with elongated slots for the shanks of screws which clamp the carriers to the head so that, if and when necessary, the bits can be moved toward or away from the axis of the bar.
German Offenlegungsschrift No. 2,533,495 discloses a boring tool wherein the front end face of the head of the boring bar is formed with teeth which mate with complementary teeth of two bit carriers. A drawback of such boring tools is that, when the tool is rotated to cause the bits to penetrate into the material of the workpiece, the resultant force which must be taken up by the teeth of the head and of the carriers invariably comprises a component which tends to lift the carriers off the head of the boring bar. Therefore, the forces which are to be applied by the means for clamping the carriers to the head of the boring bar must be increased by using extremely strong and bulky bolts or screws. Moreover, the tendency of the resultant cutting force to lift the carriers off the head of the boring bar results in wobbling of the tool when in actual use.
The heads of boring bars in certain other presently known boring tools are provided with toothed surfaces which are parallel to the axis of the boring bar. Such tools exhibit the same drawbacks as the tools wherein the toothed surfaces form part of or constitute the front end face of the head of the boring bar and wherein such front end face is normal to the axis of the bar. In other words, the resultant cutting force tends to lift the carriers off the head when the tool is in actual use.